The Submersible pump is one of several available downhole pumps, and provides a magnificent means by which fluid in a shallow well is lifted from a fluid producing strata uphole to the surface of the ground. The submersible pump will last for years if the pump is not abused. One reason this pump is preferred over a sucker rod actuated pump is because it is easily suspended on the bottom of a tubing string, and electrical wires interconnect the pump with a motor starter located at the surface of the earth, so there is hardly any maintenance required with this type pump.
In order to realize maximum efficiency in the production of liquids, whether the liquids be oil or water, it is necessary to size the downhole submersible pump with the production capacity of the payzone. In particular, in the production of oil from a shallow borehole, it is advantageous to produce the well at the maximum production rate so that the maximum drawdown is effected which causes the oil to continually migrate at a higher rate towards the production hole. This action causes a cone of depression to be formed circumferentially extending about the wellbore. It is desirable that the pump produce the payzone in this manner and yet not encounter a pump off condition, or otherwise the pump will rapidly wear and require premature replacement.
Therefore, it is advantageous to be able to produce a well for a significant length of time at a rate which eventually reaches a pump off condition, whereupon the pump is shut in for a finite time based on the production history of the well. By producing a well in this cyclic manner, the payzone is always producing the maximum amount because the well is always operating near a maximum drawdown condition.
In order to cyclically shut in a well for a predetermined time, based on the flow characteristics of the production zone, and to cyclicly produce the well until a pump off condition has been encountered, various timing means have heretofore been employed. However, this is not always acceptable because the flow characteristics of the shallow well can significantly change from time to time and this can result in the submersible pump being operated under pump off conditions for significant length of time, thereby causing irreparable damage to the pump and motor. On the other hand, if a pump off condition is not encountered during the alternate flow no-flow timed conditions, maximum draw down is not achieved and the efficiency of operation is impared.
Accordingly, it would be desirable to have made available a pump off control for a submersible pump which enables the pump to produce at a maximum rate over a long period of time without damaging the pump due to encountering a pump off condition. Method and apparatus by which this desirable goal is achieved is the subject of this disclosure.